Automatic temperature controls



June 18, 1968 A. P. KRUPER 3,388,860

AUTOMATIC TEMPERATURE CONTROLS Filed Aug. 29, 1966 FlG.l.

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saw/M m ATTORNEY United States Patent 3,388,860 AUTOMATIC TEMPERATURECONTROLS Andrew P. Kruper, Pittsburgh, Pa, assignor to WestinghouseElectric Corporation, Pittsburgh, Pa., a corporation 08 PennsylvaniaFiled Aug. 29, 1966, Ser. No. 575,626 21 Claims. (Cl. 236-1) Thisinvention relates to controls for the motors of blowers of, and for thevalves of, air cooling and heating units, and has as an object toimprove such controls.

The rooms of many modern motels, hotels, and other buildings are cooledin summer by circulating a chilled fluid from a central source throughheat exchange coils within the rooms, and are heated in winter bycirculating a heated fluid from the central source through the coils.Each coil in each room has a motor-driven blower for circulating theroom air, and each room has a thermostat which opens a valve to turn onthe cold fluid to its coil, and which closes the valve to turn oh thecold fluid to its coil, and starts and stops respectively, its blowermotor during cooling operation, and which opens a valve to turn on thehot fluid to its coil, and which closes the valve to turn off the hotfluid to its coil, and starts and stops respectively, its blower motorduring heating operation. The speeds of the blower motors can beadjusted by hand only to lo-med-hi speeds.

This invention automatically modulates the speed of such a blower motor,and the opening and closing of such a valve, in accordance with thedifference between the temperature within a room, and the setting of theroom temperature responsive means. During cooling operation, the blowerspeed and the valve opening increase with increasing room temperature,thereby providing more cooling, and decrease with decreasing roomtemperature, thereby providing less cooling. During heating operation,the blower speed and the valve opening decrease with increasing roomtemperature, thereby providing less heating, and increase withdecreasing room temperature, thereby providing more heating.

This invention will now be described with reference to the annexeddrawings, of which:

FIG. 1 is a diagrammatic view of an air conditioning system embodyingthis invention, and

FIG. 2 is a circuit schematic of the controls used for varying the speedof the blower motor, and the opening and closing of the valve, of FIG.1.

Referring first to FIG. 1 of the drawings, a conventional, centralsource 10 of cold and hot water is connected by a main supply pipe 11,and a branch supply pipe 11A, to a heat exchanger 12 in a room of amulti-room building to be cooled or heated. The heat exchanger 12 isconnected by a branch, water return pipe 13A, and a main, water returnpipe 13, to the source 10. Other heat exchangers in other rooms would beconnected by branch pipes to the pipes 11 and 13. The source 10 may becontrolled by an operator to continuously supply cold water through thepipe 11 during summer operation, and to continuously supply hot waterthrough the pipe 11 during winter operation. A blower F, driven by anelectric motor M moves room air over the surface of the heat exchanger12. A valve V of the modulating type may be connected in the pipe 11A,and may be variably Opened and closed by a conventional solenoid S.

Temperature responsive means such as NTC thermistors 16 and 17 aresupported within the room containing the heat exchanger 12. Temperatureresponsive means such as NTC thermistors 18 and 19 are in heat exchangecontact with the water supply pipe 11. NTC thermistors have negativetemperature coefiicients of resistance.

Referring now to FIG. 2 of the drawings, the motor M and the solenoid Sare connected in parallel, and to AC 3,388,860 Patented June 18, 1968supply line L1, and are connected in series with diode 22, siliconcontrolled rectifier SCR, and diode 21 to AC supply line L2. Aconventional rectifier bridge B includes the diodes 21 and 22, andseries-connected diodes 20 and 23. The junction of the diodes 20 and 22is connected through a resistor 50 to positive DC bus 24. The junctionof the diodes 21 and 23 is connected to minus DC bus 25. A Zener diode27 is connected to the busses 24 and 25, and serves as a voltageregulator.

A fixed resistor 26 is connected to the bus 24, and in series with thethermistor 18 to the bus 25. The thermistor 16 is connected to the bus24, and in series with variable resistor 28 to the bus 25. The junctionof the resistor 26 and the thermistor 18 is connected through diode 29to the junction of the thermistor 16 and the resistor 28. A. fixedresistor 30 is connected to the bus 24, and in series with capacitor 31to the bus 25. The junction of the resistor 30 and the capacitor 31 isconnected through diode 32 to the junction of the thermistor 16 and theresistor 28, and to emitter 33 of unijunction transistor 34. Baseterminal 35 of the transistor 34 is connected through fixed resistor 36to the bus 25, and to gate 46 of the silicon controlled rectifier SCR.Base terminal 37 of the transistor 34 is connected through fixedresistor 38 to the bus 24. The thermistor 17 is connected to the bus 25,and in series with variable resistor 39 to the bus 24. The junction ofthe thermistor 17 and the resistor 39 is connected through diode 40 tothe junction of the resistor 30 and the capacitor 31. The thermistor 19is connected to the bus 24, and in series with fixed resistor 41 to thebus 25. The junction of the thermistor 19 and the resistor 41 isconnected through diode 42 to the junction of the thermistor 17 and theresistor 39. Slider 42 of the resistor 28 is electrically connected tothe bus 25, and is mechanically connected by linkage 43 to slider 44 ofthe resistor 39. The slider 44 is electrically connected to the junctionof the resistor 39 and the thermistor 17. The sliders 42 and 44 can beadjusted by the linkage 43 to vary the operating points of thethermistors 16 and 17 respectively.

The thermistor 16 is the room cooling control means. The thermistor 17is the room heating control means. The resistances of the thermistors 16and 17 decrease with an increase in room temperature, and increase witha decrease in room temperature. The thermistors 18 and 19 respond to thetemperature of the water supplied through the pipe 11. Their resistancesincrease when cold water is supplied, and decrease when hot water issupplied. The thermistor 19 is used to prevent the heating controlthermistor 17 from functioning during cooling operation, and thethermistor 18 is used to prevent the cooling control thermistor 16 fromfunctioning during heating operation.

The resistor 30, the capacitor 31, the transistor 34, the siliconcontrolled rectifier SCR, the bridge B, and the motor M are connected ina conventional speed control circuit such as is disclosed in the GE SCRManual, Third Edition, page 132.

Cooling operation The water in the supply pipe 11 is cold so that theresistances of the thermistors 18 and 19 are high. The resistances ofthe cooling control thermistor 16 and the resistor 28 with which it isin series, are about equal at medium speed of the motor M, and mediumopening of the valve V. The high resistance of the thermistor 18 causesits junction with the resistor 26 to be at a higher voltage than that atthe junction of the cooling control thermistor 16 and the resistor 28 sothat the diode 29 is .back biased so that there can be no flow throughit resulting from changes in the resistance of the cooling controlthermistor 16, and there can be flow resulting.

I a from such changes, through the diode 32, to charge the capacitor 31.

The resistances of the resistor 39 and the thermistor 17 are about equalat the medium speed of the motor M, and the medium opening of the valveV. Since the thermistor 19 is cold and has a high resistance, thevoltage at the junction of the thermistor 19 and the resistor 41 islower than that at the junction of the heating control thermistorforward biased and conducts, shunting current away from the heatingcontrol thermistor 17. The voltage at the junction of the resistor 39and the thermistor 17 is lower than that at the junction of the resistor28 and the cooling control thermistor 16 so that the diode 40 is backbiased. The voltage at the junction of the resistor 30 and the capacitor31 is higher than that at the junction of the thermistor 17 and theresistor 39. Thus, the heating control thermistor 17 is effectivelydisabled.

The voltage at the junction of the cooling control thermistor 16 and theresistor 28 is equal to the resistance .of the resistor 28 divided bythe sum of the resistances of the thermistor 16 and the resistor 28,multiplied by the voltage between the busses 24 and 25. An increase inroom temperature causes the resistance of the thermistor 16 to decrease,increasing the voltage at the junction of the thermistor 16 and theresistor 28, charging through the diode 32, the capacitor 31 to a higherinitial voltage which added to the voltage applied from the positive bus24, through the resistor 30, to the capacitor 31 during each half-cycle,causes the transistor 34 to conduct earlier during each half-cycle. Whenthe transistor 34 conducts, it discharges the capacitor 31 into the gate46 of the silicon 17 and the resistor 39 so that the diode 42 iscontrolled rectifier SCR, causing the latter to conduct 7 and to supplycurrent to the motor M to speed it up conformably with the increase inroom temperature, and to supply current to the solenoid S to cause it toincrease the opening of the valve V conformably with the increase inroom temperature.

A decrease in room temperature causes the resistance of the coolingcontrol thermistor 16 to increase, decreasing the voltage at thejunction of the thermistor 16 and the resistor 28, decreasing thevoltage at the junction of the resistor 30 and the capacitor 31,charging the latter to a lower initial value so that the transistor 34is caused to conduct later during each half-cycle, causing the siliconcontrolled rectifier to conduct later during each half-cycle, decreasingthe speed of the motor M, and decreasing the opening of the valve Vconformably with the decrease in room temperature.

Heating operation The water in the supply pipe 11 is hot so that theresistances of the thermistors 18 and 19 are low. The resistances of theheating control thermistor 17 and the resistor 39 are about equal atmedium motor speed and medium valve opening. The decreased resistance ofthe thermistor 19 causes its junction with the resistor 41 to be at ahigher voltage than that at the junction of the thermistor 17 and theresistor 39 so that the diode 42 is back biased so that there can be nocurrent flow through it resulting from changes in the resistance of theheating control thermistor 17, and there can be current flow resultingfrom such changes, through the diode 40 to charge the capacitor 31.

The resistance of the resistor 28 and the thermistor 16 are about equalat medium motor speed and medium valve opening. Since the thermistor 18is hot and has a low resistance, the voltage at its junction with theresistor 26 is lower than that at the junction of the cooling controlthermistor 16- and the resistor 28, so that the diode 29 is forwardbiased and conducts, shunting current from the cooling controlthermistor 16. The voltage at the junction of the resistor 28 and thethermistor 16 is lower than that at the junction of the heating controlthermistor 17 and the resistor 39 so that the diode 32 is back biased.The voltage at the junction of the resistor 30 and the capacitor 31 ishigher than that at the junction of the thermistor 16 and the resistor28. Thus, the cooling control thermistor 16 is etfectively disabled.

The voltage at the junction of the heating control thermistor 17 and theresistor 39 is equal to the resistance of the thermistor 17 divided bythe sum of the resistances of the thermistor 17 and the resistor 39,multiplied by the voltage between the bosses 24 and 25. An increase inroom temperature causes the resistance of the thermistor 17 to decrease,decreasing the voltage at the junction of the thermistor 17 and theresistor 39, resulting in the capacitor 31 being charged through thediode 40 to a lower 7 initial voltage which added to the voltage appliedfrom the positive bus 24, through the resistor 30 during eachhalf-cycle, causes the transistor 34 and the silicon controlledrectifier SCR to conduct later during each halfcycle, thereby reducingthe speed of the motor M, and the opening of the valve V, conformablywith the increase in room temperature.

A decrease in room temperature causes the resistance of the heatingcontrol thermistor 17 to increase, increasing the voltage at thejunction of the thermistor 17 and the resistor 39, increasing thevoltage at the junction of the resistor 30 and the capacitor 31,charging the capacitor 31 to a higher initial voltage so that thetransistor 34 and the silicon controlled rectifier SCR are caused toconduct earlier during each half-cycle, and increasing the speed of themotor M, and the opening of the valve V, conformably with the decreasein room temperature.

Each room in a multi-room building served by a central source of hot andcold fluid, could have its temperature controlled as described in theforegoing in connection with a single room.

While NTC thermistors have been disclosed as temperature sensing andcontrol means, PTC thermistors, and modulating thermostats of thebellows or diaphragm type which vary electrical resistances with changesin temperature as disclosed in Patent No. 3,264,839 of J. R. Harnish,could be used with appropriate changes in the circuit of FIG. 2. Thewater temperature responsive thermistors could be replaced with on-otfthermostats with appropriate changes in the circuit of FIG. 2.

While the valve V has been disclosed as a modulating .valve, it could bean on-ofi? valve, being opened at currents above a predetermined currentthrough its solenoid S, and being closed at currents below thepredetermined current.

What is claimed is:

1. An air temperature control system comprising a heat exchanger, supplymeans for selectively supplying said exchanger with a cooling fluid or aheating fluid, a blower for moving air over the. surface of saidexchanger, an electric motor for driving said blower, electric supplyconnections, air temperature responsive means, and means including saidresponsive means connected to said motor and to said connections forincreasing the speed of said motor on an increase in air temperature,

and decreasing the speed of said motor on a decrease in air temperature,'when cooling fluid is supplied by said supply means to said exchanger,and for decreasing the speed of said motor on an increase in air'temperature, and increasing the speed of said motor on a decrease in airtemperature, when heating fluid is supplied by said supply means to saidexchanger.

2. A system as claimed in claim 1 in which said means connected to saidmotor and to said connections includes means responsive to thetemperature of the fluid supplied by said supply means to saidexchanger.

3. An air temperature control system comprising a heat exchanger, supplymeans for selectively supplying said exchanger with a cooling fluid or aheating fluid, a blower for moving air over the surface of saidexchanger, an electric motor for driving said blower, electric supplyconnections, first air temperature responsive means, second airtemperature responsive means, means for disabling said first responsivemeans when cooling fluid is supplied by said supply means to saidexchanger and for disabling said second responsive means when heatingfluid is supplied by said supply means to said exchanger, and meansincluding said second responsive means connected to said motor and tosaid connections for increasing the speed of said motor on an increasein air temperature, and decreasing the speed of said motor on a decreasein air temperature, when cooling fluid is supplied by said supply meansto said exchanger, and including said first responsive means connectedto said motor and to said connections for decreasing the speed of saidmotor on an increase in air temperature, and increasing the speed ofsaid motor on a decrease in air temperature, when heating fluid issupplied by said supply means to said exchanger.

4. A system as claimed in claim 3 in which said means for disabling saidfirst and second responsive means comprises means responsive to thetemperature of the fluid supplied by said supply means to saidexchanger.

5. An air temperature control system comprising a heat exchanger, supplymeans for selectively supplying said exchanger with a cooling fluid or aheating fluid, a blower for moving air over the surface of saidexchanger, an electric motor for driving said blower, AC supplyconnections, rectifier means, a solid-state switch connected in serieswith said rectifier means and said motor to said connections, saidswitch having a gate which causes said switch to conduct during aportion of each half-cycle when current is applied to said gate, airtemperature responsive means, and means including said responsive meansfor causing current to be applied to said gate to cause conduction ofsaid switch for longer periods of time during half-cycles on an increasein air temperature, and for causing current to be applied to said gateto cause conduction of said switch for shorter periods of time duringhalf-cycles on a decrease in air temperature, when cooling fluid issupplied by said supply means to said exchanger, and for causing currentto be applied to said gate to cause conduction of said switch forshorter periods of time during half-cycles on an increase in airtemperature, and for causing current to be applied to said gate to causeconduction of said switch for longer periods of time during half-cycleson a decrease in air temperature, when heating fluid is supplied by saidsupply means to said exchanger.

6. A system as claimed in claim 5 in which said means including saidresponsive means includes means responsive to the temperature of thefluid supplied by said supply means to said exchanger.

7. A system as claimed in claim 5 in which said means for causingcurrent to be applied to said gate includes a transistor which isarranged to supply current to said gate when said transistor conducts,and in which said means including said responsive means includes meansfor causing said transistor to conduct earlier during each half-cycle onan increase in air temperature, and to conduct later during eachhalf-cycle on a decrease in air temperature, when cooling fluid issupplied by said supply means to said exchanger, and for causing saidtransistor to conduct later during each half-cycle on an increase in airtemperature, and to conduct earlier during each half-cycle on a decreasein air temperature, when a heating fluid is supplied by said supplymeans to said exchanger.

8. A system as claimed in claim 5 in which said supply means includes afluid supply pipe connected to said exchanger, in which a valve isconnected in said pipe, in which electric means is provided foradjusting said valve towards open position on an increase in currentthrough said electric means, and for adjusting said valve towards closedposition on a decrease in current through said electric means, and inwhich said electric means is connected in series with said solid-stateswitch and said rectifier means.

9. A system as claimed in claim 8 in which said means including saidresponsive means includes means responsive to the temperature of thefluid flowing through said pipe.

10. A system as claimed in claim 7 in which said means including saidresponsive means includes means responsive to the temperature of thefluid supplied by said supply means to said exchanger.

11. An air temperature control system comprising a heat exchanger,supply means for selectively supplying a cooling fluid or a heatingfluid to said exchanger, a blower for moving air over the surface ofsaid exchanger, an electric motor for driving said blower, AC supplyconnections, rectifier means, a solid-state switch connected in serieswith said rectifier means and said motor to said connections, saidswitch having a gate which causes said switch to conduct during aportion of each half-cycle when current is applied to said gate, meansincluding a transistor arranged to apply current to said gate when saidtransistor conducts, first and second air temperature responsive means,each comprising a resistor having a resistance which varies withtemperature, means for disabling said first responsive means when acooling fluid is supplied by said supply means to said exchanger, meansfor disabling said second responsive means when a heating fluid issupplied by said supply means to said exchanger, means including saidsecond responsive means for causing said transistor to conduct earlierduring each half-cycle on an increase in air temperature, and to conductlater during each half-cycle on a decrease in air temperature, whencooling fluid is supplied by said supply means to said exchanger, andmeans including said first responsive means for causing said transistorto conduct later during each half-cycle on an increase in airtemperature, and to conduct earlier during each half-cycle on a decreasein air temperature, when a heating fluid is supplied by said supplymeans to said exchanger.

12. A system as claimed in claim 11 in which said supply means includesa fluid supply pipe connected to said exchanger, in which a valve isconnected in said pipe, in which electric means is provided foradjusting said valve towards open position on an increase in currentthrough said electric means, and for adjusting said valve towards closedposition on a decrease in current through said electric means, and inwhich said electric means is connected in series with said solid-stateswitch and said rectifier means.

13. A system as claimed in claim 12 in which said disabling meansincludes means responsive to the temperature of the fluid supplied bysaid supply means through said pipe to said exchanger.

14. A system as claimed in claim 11 in which said disabling meansincludes means responsive to the temperature of the fluid supplied bysaid supply means to said exchanger.

15. A system as claimed in claim 14 in which said first and secondresponsive means are thermistors.

16. A system as claimed in claim 13 in which said first and secondresponsive means are thermistors.

17. A system as claimed in claim 11 in which said first and secondresponsive means are thermistors.

18. An air temperature control system comprising a heat exchanger,supply means for selectively supplying a cooling fluid or a heatingfluid to said exchanger, a blower for moving air over the surface ofsaid exchanger, an electric motor for driving said blower, AC supplyconnections, rectifier means, a solid-state switch connected in-serieswith said rectifier means and said motor to said connections, saidswitch having a gate which causes said switch to conduct during aportion of each half-cycle when current is applied to said gate, acapacitor, a transistor connected to said capacitor and said gate so asto discharge said capacitor into said gate when said transistorconducts, said transistor having a control electrode connected to saidcapacitor, means for supplying a DC Voltage during each half-cycle tosaid control elec trode, first and second air temperature responsivethermistors, means including said second thermistor for providing aninitial voltage on said capacitor which increases sponsive to thetemperature of the fluid supplied by said supply means to saidexchanger, means including said third thermistor for disabling saidfirst thermistor when cooling fluid is supplied by said supply means tosaid exchanger, and means including said fourth thermistor for disablingsaid second thermistor when heating fluid is supplied by said supplymeans to said exchanger.

19. A system as claimed in claim 18 in which said supply means includesa fluid supply pipe connected to said exchanger, in which a valve isconnected in said pipe, in which electric means is provided foradjusting said valve towards open position on an increase in currentthrough said electric means, and for adjusting said valve towards closedposition on a decrease in current through said electric means, and inwhich said electric means is connected in series with said solid-stateswitch and said rectifier means.

23. An air temperature control system comprising a heat exchanger,supply means including a fluid supply pipe for selectively supplying acooling fluid or a heating fluid to said exchanger, a valve in saidpipe, electric means for adjusting said valve towards open position onan increase in current through said electric means and for adjustingsaid valve towards closed position on a decrease in current through saidelectric means, AC supply connections, rectifier means, a solid-stateswitch connected in series with said rectifier means and said electricmeans to said connections, said switch having a gate which causes saidswitch to conduct during a portion of each half-cycle when current isapplied to said gate, means including a transistor arranged to applycurrent to said gate when said transistor conducts, first and second airtemperature responsive means, each comprising a resistor having aresistance which varies with temperature, means for disabling said firstresponsive means when a cooling fluid is supplied by said supply meansto said exchanger, means for disabling said second responsive means whena heating fluid is supplied by said supply means to said exchanger,means including said second responsive means for causing said transistorto conduct earlier during each half-cycle on an increase in airtemperature, and to conduct later during each half-cycle on a decreasein air temperature, when cooling fluid is supplied by said supply meansto said exchanger, and means including said first responsive means forcausing said transistor to conduct later during each half-cycle on anincrease in air temperature, and to conduct earlier during eachhalf-cycle on a decrease in air temperature, when a heating fluid issupplied by said supply means to said exchanger.

21. A system as claimed in claim 20 in which said responsive means arethermistors, in which said means for disabling said second responsivemeans comprises a third thermistor responsive to the temperature of thefluid supplied by said supply means to said exchanger, and in which saidmeans for disabling said first responsive means comprises a fourththermistor responsive to the temperature of the fluid supplied by saidsupply means to said exchanger.

References Cited UNITED STATES PATENTS 3,196,629 7/1965 Wood 621833,211,214 10/1965 Chambers 236-78 X EDWARD J. MICHAEL, Primary Examiner.

1. AN AIR TEMPERATURE CONTROL SYSTEM COMPRISING A HEAT EXCHANGER, SUPPLYMEANS FOR SELECTIVELY SUPPLYING SAID EXCHANGER WITH A COOLING FLUID OR AHEATING FLUID, A BLOWER FOR MOVING AIR OVER THE SURFACE OF SAIDEXCHANGER, AN ELECTRIC MOTOR FOR DRIVING SAID BLOWER, ELECTRIC SUPPLYCONNECTIONS, AIR TEMPERATURE RESPONSIVE MEANS, AND MEANS INCLUDING SAIDRESPONSIVE MEANS CONNECTED TO SAID MOTOR AND TO SAID CONNECTIONS FORINCREASING THE SPEED OF SAID MOTOR ON AN INCREASE IN AIR TEMPERATURE,AND DECREASING THE SPEED OF SAID MOTOR ON A DECREASE IN AIR TEMPERATURE,WHEN COOLING FLUID IS SUPPLIED BY SAID SUPPLY MEANS TO SAID EXCHANGER,AND FOR DECREASING THE SPEED OF SAID MOTOR ON AN INCREASE IN AIRTEMPERATURE, AND INCREASING THE SPEED OF SAID MOTOR ON A DECREASE IN AIRTEMPERATURE, WHEN HEATING FLUID IS SUPPLIED BY SAID SUPPLY MEANS TO SAIDEXCHANGER.